The present invention relates to a thread chain sewing method and device for use in the two-needle overlock sewing machine.
When over-edging the edge of a fabric material with the overlock sewing machine, continuous thread chains connected to the fabric material are formed at the finish of sewing. In the case of one-needle overlock sewing machines in which three threads are used, a thread chain holding and cutting means is arranged on the operator's side of the needle drop point. When sewing is finished, continuous thread chains connected to the fabric material are shifted toward the operator to be held by the thread chain holding and cutting means, and are then cut off from the fabric material. Therefore, thread chains held by the thread chain holding and cutting means can be atuomatically folded and sewn into the seam of a subsequent section of fabric material, thus preventing the seam from being frayed at the beginning of the seam without requiring the back-tacking operation of a back-tacking machine.
However, the two-needle overlock sewing machine could not smoothly attain the automatic sewing of thread chains into the seam. Automatic folding and sewing of thread chains into the seam requires that the thread chains previously formed and entangled around the chaining-off fingers be folded and sewn into the seam as the next fabric segment is sewn. The two-needle over-lock sewing machine has two needles, and chaining-off fingers are arranged at one side of the needle drop point of each needle, that is, the inner and outer chaining-off fingers are arranged side by side, one on either side of the needle drop point of the outer needle. Therefore, in the case of the two-needle overlock sewing machine, thread chains formed before the sewing process reaches the fabric material are normally wrapped around the inner and outer chaining-off fingers. As the result, thread chains held by the thread chain holding and cutting means are sewn together with newly formed thread chains. Or when being folded and sewn into the seam, thread chains are sewn to the fabric material by the thread of the outer needle and the subsequent folding and sewing of thread chains into the seam is not carried out, leaving almost all of the thread chain projecting at the beginning of the seam.
In order to eliminate these drawbacks, the inventors of the present invention have developed a thread chain sewing method and device for use in the two-needle overlock sewing machine wherein the inner chaining-off finger, which was conventionally fixed alongside the outer chaining-off finger, is retractable in a direction opposite the fabric material feeding direction and held in its retracted position during the non-sewing time. Thread chains formed before the sewing process reaches the fabric material are wrapped only around the outer chaining-off finger without bridging both inner and outer chaining-off fingers, thus preventing previously formed thread chains from being sewn to the fabric material by thread of the outer needle at the time the sewing process reaches the fabric segment and allowing thread chains to be smoothly folded and sewn into the seam.
However, according to tests conducted using the device, it has become apparent that if the inner chaining-off finger is retracted at the moment when the sewing process is finished, that is, at the time when the trailing end of fabric material has passed through the needle drop points, thread chains formed after the sewing process are not wrapped around the inner chaining-off finger, thus making it impossible to form symmetrical and beautiful thread chains and to fold and sew thread chains into the seam beautifully at the time the sewing process is applied to a subsequent segment of fabric material.